Planking panel for a structural component, flow body comprising such a planking panel and device for monitoring material damage on such a planking panel

ABSTRACT

The invention pertains to a planking panel (B) for a structural component ( 1 ) that is realized in the form of a sandwich component in its inner region (BI) that extends in a planar fashion and features a first skin section ( 11 ), a second skin section ( 12 ) and a core section ( 13 ) that is situated between these two skin sections, wherein the core section ( 13 ) connects the first and the second skin sections ( 11, 12 ) to one another in a planar fashion, with the invention being characterized in that a plurality of monitoring lines ( 14 ) is provided that extend over a planar section of the core section ( 13 ) to be monitored in order to detect damage in the core section ( 13 ) and respectively feature a first connection point ( 15 ) on a first end ( 14   a ) and a second connection point ( 16 ) on a second end ( 16   a ) in order to apply a monitoring signal (UK), wherein the monitoring lines ( 14 ) have a tear strength that lies in the range between 50% and 100% of the tear strength of the core section ( 13 ).

This patent application claims the filing date of German patentapplications DE 10 2010 027 696.0, DE 10 2010 027 695.2, DE 10 2010 031688.1 and DE 10 2010 031 690.3 and of U.S. provisional patentapplications 61/365,857, 61/365,882, 61/365,873 and 61/365,863, all ofwhich were filed on Jul. 20, 2010. Due to the above reference, thedisclosures of these patent applications are incorporated into thepresent patent application.

The invention pertains to a planking panel for a structural componentthat is realized in the form of a sandwich component in its inner regionthat extends in a planar fashion and features a first skin section, asecond skin section and a core section situated between these two skinsections, wherein the core section connects the first and the secondskin sections to one another in a planar fashion, as well as to a flowbody with such a planking panel and a device for monitoring materialdamage on a planking panel.

Planking panels of this type are known from the prior art and used ascovering components for the design of surfaces in various branches ofindustry. Due to the simple structure, these components make it possibleto realize a large variety of different surface shapes such thatcomponents of this type are suitable, for example, for use as interiorcovering in vehicles. However, such sandwich components have thedisadvantage that the relatively soft core section is susceptible totearing under mechanical loads, particularly impact loads. Since thecore section is covered by skin sections on both sides, it is difficultto determine if the component is damaged without subjecting thecomponent to destructive testing.

Particularly in the field of manned aviation, the operatability of theaircraft and therefore the structural integrity of the componentsinstalled therein play an important role. An undetectable criticaldamage of a safety-relevant component can lead to the failure of varioustechnical systems and therefore have catastrophic consequences. In theaircraft industry, safety-relevant components therefore are inspected,repaired and possibly replaced if the damage can no longer beeconomically repaired within predefined intervals, namely in accordancewith a maintenance schedule. The planking of an aircraft is continuouslysubjected to possible collisions with other bodies during flyingoperations. The aircraft is frequently hit by rocks, hailstones duringthunderstorms or even birds that get into the flight path of theaircraft. The impact of such a foreign body or part thereof on aplanking element realized in the form of a sandwich structure must becategorized is particularly critical because the deformation, to whichthe sandwich element is subjected, can cause the foam core in theinterior to tear or to separate from the surrounding skin sectionswithout such damage being visible from outside.

This is the reason why such sandwich components have so far not beenused as safety-relevant components of the planking in the constructionof aircraft, particularly in commercial aviation.

It is the objective of the invention to disclose a planking panel for astructural component with the lowest weight possible, a flow body withsuch a planking panel and a device for monitoring material damage on aplanking panel that can be used for the main-load bearing region of asafety-critical component structure.

This objective is attained with the characteristics of the independentclaims. Other embodiments are disclosed in the dependent claims thatrefer to these independent claims.

The inventive solutions allow the non-destructive testing (NonDestructive Testing) of a planking panel and, in particular, thereliable detection of all types of damages.

According to the inventive solution of a planking panel, it is proposedto form the core section of a planking panel realized in the form of asandwich structure of foam material and to utilize this planking panelin a main-load bearing region of the aircraft structure despite itssusceptibility. However, the integrity of the material of the coresection (structural integrity) is checked by means of at least onemonitoring line with a tear strength that in terms of its amount islower than the fracture strength of the planar region of the coresection such that damage in the core section can be detected in anon-destructive, simple and reliable fashion. In this way, the plankingpanel can be used as damage-tolerant planking panel such that it issuitable, in particular, for use as part of an aircraft structure.

The term main-load bearing region refers to a region of the aircraftstructure, the damage of which can lead to a catastrophic event for theaircraft during the flight if the damage occurs in such a way that thisregion is no longer able to withstand tensions resulting from the mainloads being applied to the aircraft structure.

The invention proposes a planking panel for a structural component thatis realized in the form of a sandwich component in its inner region thatextends in a planar fashion and features a first skin section, a secondskin section and a core section that is situated between these two skinsections and connects the first and the second skin sections to oneanother in a planar fashion. In order to detect damages in a fictitiousmonitoring volume of the core section that is respectively monitoredwith respect to the presence of damage, at least one monitoring line isprovided in this monitoring volume or a plurality of monitoring linesextending over the monitoring volume of the core section to be monitoredis provided. Depending on the respective application, the monitoringline or the monitoring lines is/are arranged in the monitoring volume insuch a way that damage monitoring of the monitoring volume can berealized. Each monitoring line may respectively feature a firstconnection point at a first end and a second connection point at asecond end in order to apply a monitoring signal. Alternatively, oneconnection point may be coupled to several monitoring lines. In thiscase, the monitoring lines have a tear strength that lies, inparticular, in the range between 50% and 100% of the tear strength ofthe core section.

Such an arrangement provides the advantage that defects in the coresection of the planking panel can be detected immediately after theyoccur and a defective component can be very quickly identified as suchin order to be subsequently replaced.

In another embodiment of the invention, the tear strength of themonitoring lines lies in the range between 80% and 100% of the tearstrength of the core section, but it is particularly referred that thetear strength of the monitoring lines lies in the range between 90% and100% or 90% and 95% of the tear strength of the core section.

Furthermore, the core section may have a tensile strength in the rangebetween 1.5 MPa and 2.5 MPa and/or a shear strength in the range between0.8 MPa and 1.6 MPa.

According to an embodiment of the invention, it is proposed that atleast one monitoring line within the monitoring volume extends in theplanking panel in a meander-shaped fashion such that bridging segmentsextending along the thickness direction of the planking panel andbetween the oppositely arranged skin sections and reversing segmentsthat respectively connect these bridging segments and are respectivelysituated in one of the oppositely arranged skin sections are formed,wherein reversing segments that lie behind one another in thelongitudinal direction of the monitoring line are situated in differentskin sections. In this case, the connection points of the at least onemonitoring line may be situated in different skin sections or in one andthe same skin section.

Furthermore, a plurality of monitoring lines may extend in a thicknessdirection of the planking panel, wherein each monitoring line featurestwo connection points, and wherein a first connection point is situatedon the first skin section and a second connection point is situated onthe second skin section.

Due to this arrangement, the formation of tears in the core section thatextend transverse to the thickness direction can be detected in aparticularly simple fashion.

According to an embodiment of the invention, each monitoring linefeatures two connection points. According to another embodiment, atleast one connection point is provided and coupled to several monitoringlines.

In another embodiment of the present invention, a plurality ofmonitoring lines may extend in a longitudinal direction of the plankingpanel, wherein each monitoring line features two connection points, bothof which are situated on the first skin section or both of which aresituated on the second skin section.

Due to this arrangement, the formation of tears in the core section thatextend along the thickness direction and therefore transverse to thelongitudinal direction of the planking panel can be detected in aparticularly simple fashion.

Furthermore, the monitoring lines may consist of electrical conductors,the connection points may consist of electrical connection points andthe monitoring signal may be an electric monitoring voltage signal.

This provides the advantage that the monitoring voltage can berespectively applied to one electrical conductor. If a current flow doesnot takes place in the conductor or deviates from a predefined currentvalue, it can be determined that the conductor and therefore also thecore section is damaged.

The monitoring lines may furthermore and/or additionally consist ofoptical waveguides, the connection points may consist of opticalconnection points and the monitoring signal may be an optical monitoringsignal.

The utilization of optical waveguides as monitoring lines provides theadvantage that, in contrast to electrical conductors, no interferencesignals originating, for example, from magnetic fields are induced suchthat the damage detection can also be reliably carried out in magneticfields. This is particularly advantageous when the aircraft fliesthrough a thunderstorm, in which lightning strikes that generatemagnetic fields occur.

Furthermore, the monitoring signal may be permanently applied to themonitoring lines or the monitoring signal may be applied to themonitoring lines for a predefined time period within predefined timeintervals.

The first variation provides the advantage that damage can beimmediately detected. If a monitoring signal is permanently applied, aline interruption leads to an immediate signal loss and therefore to anintermediate defect detection. The second alternative provides theadvantage of a consistent inspection activity for maintenance personnelin terms of conduct such that the maintenance activities can be moreprecisely defined and optimized. Furthermore, a measurement in thedormant state is in most instances more reliable than in the operatingstate.

According to an inventive embodiment, the core section of the plankingpanel is formed of a homogenous material.

Furthermore, the core section may consist or be formed of a foam coreand, in particular, an aluminum foam core, a ceramic core or a sandwichcore. According to another embodiment, the core section itself featuresan intermediate layer and/or is realized in the form of a composite corethat is composed of several sandwich cores.

Furthermore, the tear strength of the monitoring lines may correspond toa tensile strength in the range between 1.5 MPa and 2.5 MPa and a shearstrength between 0.8 MPa and 1.6 MPa.

Another aspect of the present invention concerns a flow body,particularly for an aircraft, with a planking panel.

According to another exemplary embodiment, a device for monitoringmaterial or structural damage on a planking panel is proposed, whereinthe monitoring device features an activation device for transmitting asignal via the monitoring line and an evaluation device, by means ofwhich it can be determined if the monitoring line is intact based on thesignal transmitted via the monitoring line in order to detect damage inthe foam section, wherein the activation device is designed in such away that it transmits the monitoring signal via the monitoring linespermanently or within predefined time intervals.

Exemplary embodiments of the invention are described below withreference to the attached schematic figures, in which:

FIG. 1 shows a top view of a section of an aircraft tail unit with aninventive planking panel,

FIG. 2 shows a partial section through an inventive planking panelaccording to a first embodiment of the invention, in which the plankingpanel features a monitoring line extending in the longitudinal directionof the core section in order to detect damage in a monitoring volume ofthe core section,

FIG. 3 shows a partial section through an inventive planking panelaccording to another embodiment of the invention, in which the plankingpanel features a monitoring line that extends in the core layer in ameander-shaped fashion, wherein the connection devices coupled to thismonitoring line are respectively provided on different skin sections,

FIG. 4 shows a partial section through an inventive planking panelaccording to another embodiment of the invention, in which the plankingpanel features a monitoring line that extends in the core layer in ameander-shaped fashion, wherein the connection devices coupled to thismonitoring line are respectively provided on the same skin section,

FIG. 5 shows a partial section through an inventive planking panel withseveral variations of the arrangement of the monitoring lines,

FIG. 6 shows a partial section through an inventive planking panelaccording to a second embodiment, and

FIG. 7 shows another partial section through an inventive plankingpanel.

FIG. 1 shows a structural component 1 with a plurality of inventiveplanking panels B that at least partially form a surface of thestructural component 1. The structural component 1 may comprise a flowbody 1 such as, for example, a tail unit of an aircraft, particularly anaircraft wing, an elevator, a rudder or a part of the aircraft fuselage.

A coordinate system is illustrated for orientation purposes andrespectively defines a chord direction T, a wingspan direction S and athickness direction D of the aircraft wing or the structural componentand therefore of the planking panel B.

This coordinate system is also illustrated in FIG. 2 that shows acollision of a foreign body F with the planking element B. FIG. 2 showsa partial section along a line of section that extends in a planedefined by the thickness direction D and the wingspan direction S inFIG. 1. The planking element B features a first skin section 11 in itsupper region referred to the thickness direction D and a second skinsection 12 in its oppositely arranged lower region referred to thethickness direction D. The skin sections 11, 12 have a small thicknessin comparison with their lateral dimensions and therefore form planar,panel-shaped bodies. A core layer 13 provided between the first skinsection 11 and the second skin section 12 has a greater thickness thanthe skin sections 11, 12. On its upper surface, the core layer 13 is inplanar contact with the first skin layer 11. The core layer 13 isfurthermore in planar contact with the second skin layer 12 on its lowersurface. The planar contact can be additionally intensified, forexample, by providing an adhesive between the core layer and the skinlayer or by producing screwed or riveted connections. According to FIG.1, the planking panels B feature an inner region IB, in which themonitoring lines 14 extend.

In the first embodiment of the invention illustrated in FIG. 2, amonitoring line 14 extends through the core layer 13 of the plankingpanel B in a longitudinal direction of the planking panels B. Themonitoring line 14 has a first end 14 a and a second end 14 b, whereinthe first end 14 a is connected to a first connection point 15 and thesecond end 16 a is connected to a second connection point 16. Bothconnection points 15, 16 are arranged in the first skin layer 11, butcould also be arranged in the second skin layer 12 in an alternativeembodiment of the invention. A monitoring signal can be externallyapplied to the monitoring line 14 via the connection points 15, 16,wherein the monitoring signal is transmitted from the first connectionpoint 15 to the second connection point 16 or vice versa.

The monitoring lines 14 used may consist of electrical conductors oroptical waveguides such as, for example, fiber optic cables. Amonitoring signal corresponding to these lines then needs to be appliedin the form of an electrical or optical signal. An external diagnosticsystem or an internal diagnostic system arranged in the planking panel Bdetermines if the applied signal is transmitted via the monitoring line14. The utilization of electrical conductors makes it possible tomanufacture particularly cost-efficient planking elements B, wherein thehigh robustness of the electrical conductors reduces the effort for themanufacturing process of the planking panels B. The utilization ofoptical monitoring lines provides the advantage that the planking panelsB are insensitive to electromagnetic interferences.

FIG. 7 shows a first embodiment of the invention, wherein this figureshows an exemplary tear R formed as a result of the impact of theforeign body F according to FIG. 2. This impact leads to a deflection ofthe entire planking panel B, wherein the core section 13 in the interiorof the panel is subjected to a tensile stress that acts in itslongitudinal direction. The core section 13 tears if this tensile stressexceeds a maximum material value such that the tear shown is formed. Themonitoring line 14 extends along the longitudinal direction of theplanking panel B and has a tear strength that is essentially identicalto the tear strength of the material of the core section 13. This meansthat tearing of the core section 13 directly leads to an interruption ofthe monitoring line 14. A signal transmission therefore cannot takeplace and the diagnostic device detects a defect. In FIG. 7, amonitoring voltage Uk is applied to the monitoring lines 14 at theconnection points 15, 16 such that a monitoring signal in the form of apredefined current intensity flows through the monitoring line 14.

However, a signal transmission does not have to completely fail in orderto detect damage. In an alternative embodiment of the invention, amonitoring signal may be applied in the form of an electric voltage UKthat generates a current flow with a predefined current value in themonitoring line 14. If the diagnostic device measures a current flowwith the predefined current value, it is determined that no damageexists. However, if a current value is detected that deviates from thepredefined current value, it is determined that the planking panel B isdamaged. This embodiment naturally can be combined with the embodiment,in which only the current value “zero” defines a damage scenario.

The monitoring signal may flow through the monitoring line 14permanently or in a pulsed fashion. When the monitoring line 14 isinterrupted, a signal transmission no longer takes place beginning atthe time of its interruption, wherein this is immediately detected bythe diagnostic device that simultaneously also outputs the monitoringsignal. In a pulsed signal application, the diagnostic device determinesthat damage exists on the planking panel B by means of the first signalthat is applied to the monitoring line 14 after a damage scenario andcannot be transmitted. In this way, energy can be saved in comparisonwith a permanent signal transmission.

The monitoring lines 14 have a tear strength that is adapted to thematerial properties of the core section 13. In this respect, the tearstrength lies in the range between 50% and 100%, preferably between 80%and 100%, particularly between 90% and 100%, of the tear strength of thematerial of the core section 13. This makes it possible to ensure thatthe monitoring line 14 is also destroyed when the core section 13suffers damage in the form of a tear. In another preferred embodiment ofthe present invention, the tear strength of the monitoring line 14 liesin the range between 80% and 95% of the tear strength of the material ofthe core section 13. This embodiment provides the advantage that themonitoring line 14 is also severed in the corresponding region even ifthe core section 13 was not yet damaged, but rather merely subjected toa load that lies in the fringe load range of its material, wherein thediagnostic system consequently detects that the planking panel B was atleast subjected to a load in the fringe range. Subsequently, thediagnostic device can output a warning message in advance such that theplanking panel B can be replaced before an actual damage scenariooccurs.

The tear strength of the monitoring lines 14 preferably corresponds to atensile strength that lies between 1.5 MPa and 2.5 MPa, but preferablyamounts, in particular, to 1.9 MPa, and/or a shear strength that liesbetween 0.8 MPa and 1.6 MPa, but preferably amounts to 1.15 MPa.

FIG. 5 shows several variations of the arrangement of the monitoringlines 14, wherein the connection points 15, 16 of the monitoring lines14 do not necessarily have to be provided on the same skin section. Themonitoring lines 14 may extend from a first skin section 11 to a secondskin section 12 essentially parallel to the thickness direction D. Theskin sections 11, 12 may alternatively or additionally also be arrangedvertically such that the monitoring lines 14 extend essentially parallelto the chord direction T. FIG. 5 furthermore shows an exemplary tear Rthat conceivably could be formed after the impact of a foreign body F asillustrated in FIG. 1. The tear intersects with at least one of themonitoring lines 14 such that a signal transmission is no longerpossible along these severed monitoring lines 14.

FIG. 6 shows another embodiment of the present invention, wherein thestructure of the planking panel B in the form of a sandwich component isidentical to that described with reference to FIG. 1. However, themonitoring lines 14 extend from the first skin section 11 to the secondskin section 12 and are provided at predefined critical points K of theplanking panel B in this case. A tear shown extends essentially parallelto the skin sections 11, 12 and therefore transverse to the monitoringlines 14. A foreign body F that laterally impacts on the planking panelB generates an impulse that is illustrated in the form of the vectors FKand leads to a compression of the planking panel B. The effective forcecauses the skin sections 11, 12 to deflect, namely away from the coresection 13, such that the tear R shown is formed. In this case, the tearR also severs the monitoring lines 14 such that the monitoring signalscan no longer be transmitted and the diagnostic device determines thatthe planking panel has been damaged.

The monitoring lines or arrangement of monitoring lines provided in themonitoring volume KV in accordance with the invention may extenddifferently within the monitoring volume VK. FIG. 3 shows a preferredembodiment of the invention, in which the planking panel B features amonitoring line 14 that extends in the core layer or the core section 13in a meander-shaped fashion, wherein the connection devices 15, 16coupled to this monitoring line 14 are respectively provided ondifferent skin sections 11 and 12. FIG. 4 shows a variation of thisembodiment, in which the planking panel B features a monitoring line 14that extends in the core layer or the core section 13 in a meandershaped fashion, wherein the connection devices 15, 16 coupled to thismonitoring line 14 are respectively provided on the same skin section 11or 12.

1. A planking panel for a structural component that is realized in theform of a sandwich component in its inner region that extends in aplanar fashion and features a first skin section, a second skin sectionand a core section that is situated between these two skin sections andconnects the first and the second skin sections to one another in aplanar fashion, wherein the planking panel features at least onemonitoring line that is respectively coupled to a first connection pointand to a second connection point in order to apply a monitoring signaland extends over a region of the core section in order to detect damagein a monitoring volume of the core section, wherein the monitoring linehas a tear strength that in terms of its amount lies in the rangebetween 50% and 100% of the amount of the fracture strength of theplanar region of the core section.
 2. The planking panel according toclaim 1, wherein the core section has a tensile strength in the rangebetween 1.5 MPa and 2.5 MPa and/or a shear strength in the range between0.8 MPa and 1.6 MPa.
 3. The planking panel according to claim 1, whereinat least one monitoring line extends in the planking panel in ameander-shaped fashion such that bridging segments extending along thethickness direction of the planking panel and between the oppositelyarranged skin sections and reversing segments that respectively connectthese bridging segments and are respectively situated in one of theoppositely arranged skin sections are formed.
 4. The planking panelaccording to claim 3, wherein the connection points of the at least onemonitoring line are situated in different skin sections.
 5. The plankingpanel according to claim 3, wherein the connection points of the atleast one monitoring line are situated in one and the same skin sectionof the skin sections.
 6. The planking panel according to claim 1,wherein the planking panel features a plurality of monitoring lines thatextend along the thickness direction of the planking panel, wherein eachmonitoring line features two connection points, and wherein a firstconnection point is respectively situated on the first skin section anda second connection point is respectively situated on the second skinsection.
 7. The planking panel according to claim 1, wherein theplanking panel features a plurality of monitoring lines that extendalong the longitudinal direction of the planking panel and eachmonitoring line features two connection points, both of which aresituated on the first skin section or both of which are situated on thesecond skin section.
 8. The planking panel according to claim 1, whereinthe monitoring lines consist of electrical conductors, the connectionpoints consist of electrical connection points and the monitoring signalconsists of an electric monitoring voltage.
 9. The planking panelaccording to claim 1, wherein the monitoring lines consist of opticalwaveguides, the connection points consist of optical connection pointsand the monitoring signal consists of an optical monitoring signal. 10.The planking panel according to claim 1, wherein the core sectionconsists of a homogenous material that preferably is specificallylighter than the two skin sections.
 11. The planking panel according toclaim 1, wherein the core section consists of a foam core, particularlya polymer foam core, an aluminum foam core, a ceramic core or a massivecore.
 12. The planking panel according claim 1, characterized in thatthe core section consists of a composite core that is composed ofseveral sandwich cores.
 13. The planking panel according to claim 1,characterized in that the tear strength of the monitoring linescorresponds to a tensile strength in the range between 1.5 MPa and 2.5MPa and a shear strength between 0.8 MPa and 1.6 MPa.
 14. A flow body,particularly for an aircraft, with a planking panel according toclaim
 1. 15. A device for monitoring material damage on a planking panelin accordance with claim 1, wherein the monitoring device features anactivation device for transmitting a signal via the monitoring line andan evaluation device, by means of which it can be determined if themonitoring line is intact based on the signal transmitted via themonitoring line in order to detect damage in the foam section, whereinthe activation device is designed in such a way that it transmits themonitoring signal via the monitoring lines permanently or withinpredefined time intervals.